1. Field of the Invention
The present invention relates to a head drum assembly for a tape recorder such as a VCR or a camcorder, and in particular, to a method of preloading a head drum bearing in a head drum assembly of a tape recorder.
2. Description of the Related Art
In general, tape recorders such as VCRs and camcorders are provided with a head drum assembly that is mounted for high-speed rotation. This enables information to be recorded and reproduced by the scanning of a magnetic head in relation to a magnetic tape. As shown in FIG. 1, which is a partial cross-sectional schematic view of a head drum assembly, the head drum assembly comprises: a rotary drum 10 which rotatably supports a magnetic head H for recording/reproducing information by scanning a running magnetic tape; a fixed drum 20 which is press-fitted onto a lower part of a shaft 30 engaged in a central axial bore of the rotary drum 10; and an upper bearing 40 and a lower bearing 50 located one on the other and press-fitted between the rotary drum 10 and the shaft 30. In the drawing, reference numerals 1 and 2 indicate a rotor and a stator, respectively, and reference numeral 3 indicates a magnet mounted on the internal circumferential surface of the rotor 1.
The head drum assembly of a tape recorder with the above-mentioned construction is provided with preloading means for applying preload to the upper bearing 40 and the lower bearing 50, and the conventional bearing preloading means generally employs a preloading construction as shown in FIG. 1, in which a preloading boss 60 is provided above the upper bearing 40. A rib 70 is provided on the fixed drum 20 below the lower bearing 50, thereby applying preload to the bearings.
According to conventional bearing preloading construction, the preloading boss 60 is secured by a set screw S so that a projection formed in the preloading boss 60 downwardly compresses the internal race 41 (not shown) of the upper bearing 40. The rib 70 is made to upwardly compress the internal race 51 (not shown) of the lower bearing, thereby applying preload to the bearings.
Accordingly, the preloading construction of the conventional head drum assembly has a problem in that the preloading boss 60 and the set screw for securing the boss are additionally required components, thereby increasing the cost. In addition, there is also a problem in that, because it is not easy to determine the position for securing the preloading boss 60 when engaging the set screw S, it is difficult to precisely control the preload. This can lead to problems such as the generation of noise while driving the bearings.
Furthermore, according to the bearing preloading method and construction of the conventional head drum assembly, it is required that the head drum assembly be subjected to a heat treatment process (such as annealing) after the bearings are assembled. This removes thermal deformation caused by the excessive press-fitting of the bearings. Therefore, there is also a problem in that manufacturing productivity is lowered and the costs of manufacturing are increased.